76 lines
2 KiB
Markdown
76 lines
2 KiB
Markdown
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---
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tags: [python, OOP]
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---
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# Class inheritance in Python
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We distinguish the **parent/source/superclass** class and the **subclass** that
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**extends** it.
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A subclass can have more than one parent class that it extends, but this is
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atypical.
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> The subclass will inherit all attributes and methods of the superclass unless
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> it overrides them.
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In addition to overriding the methods of the parent we can extend them in the
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child. This is a bit like using an abstract.
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## Example of class inheritance
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```py
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class Person:
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""" Our superclass
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"""
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def __init__(self, name, age):
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self.name = name
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self.age = age
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def birthday(self):
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print('Happy birthday you were', self.age)
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self.age += 1
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print('You are now', self.age)
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def __str__(self):
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return self.name + ' is ' + str(self.age)
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class Employee(Person):
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""" Our subclass that extends `Person`
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"""
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def __init__(self, name, age, id):
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super().__init__(name, age)
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self.id = id
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def calculate_pay(self, hours_worked):
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rate_of_pay = 7.50
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if self.age >= 21:
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rate_of_pay += 2.50
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return hours_worked * rate_of_pay
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def __str__(self):
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return super().__str__() + ' - id(' + str(self.id) + ')'
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```
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### Key points
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- We pass the name of the parent class to the child class as a parameter
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- We must include all of the parent class's attributes in the constructor of the
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subclass
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- We must use a special `super().__init__(..,...)` method to enact the extension
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of the parent. This method references the `__init__` class in the parent.
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## Protected/private methods and attributes
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> Protected methods and attributes are private to the class but can be accessed
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> from any subclass
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> Private methods cannot be accessed from anywhere outside of the class
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We declare private methods and attributes with a double underscore (`__`). We
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declare protected methods and attributes with a single underscore (`_`).
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This is **convention**, there are not actually private and protected attributes
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or properties.
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